Parents often turn to educators and healthcare professionals for advice on how to best support their child's language development. These professionals frequently suggest implementing the "one-parent-one-language" approach to ensure consistent exposure to both languages. The goal of this study was to understand how language exposure influences the receptive vocabulary development of simultaneous bilingual children. To this end, we targeted nine German-French children growing up in bilingual families. Their exposure to each language within and outside the home was measured, as were their receptive vocabulary abilities in German and French. The results indicate that children are receiving imbalanced exposure to each language. This imbalance is leading to a slowed development of the receptive vocabulary in the minority language, while the majority language is keeping pace with monolingual peers. The one-parent-one-language approach does not appear to support the development of both of the child's languages in the context described in the present study. Bilingual families may need to consider other options for supporting the bilingual language development of their children. As professionals, we need to provide parents with advice that is based on available data and that is flexible with regards to the current and future needs of the child and his family. (Contains 3 tables.)